Block distortion detection method, block distortion detection apparatus, block distortion removal method, and block distortion removal apparatus

Abstract

A video decoder is connected with a block distortion detector for specifying the boundary of blocks where block boundary occurs, using decoded image data and information of motion vectors, which are supplied from the video decoder; and a block distortion remover for subjecting pixels in the vicinity of the block boundary of the decoded image to filtering on the basis of the result of detection from the block distortion detector, thereby removing the block distortion. Therefore, block distortion is accurately detected when a compressed and coded image is decoded, and the detected block distortion is removed while minimizing the blurriness of the image.

1. A block distortion removal method for removing block distortion included in the decoded image obtained by decoding the code sequences which are obtained by dividing an image into blocks each comprising plural pixels to be coded including:
 a first decision step which decides the strength of the block distortion at the block boundary: 
 a second decision step which decides the necessity or the innecessity of the removal of the block distortion by using the decision result by said first decision step; and 
 a block distortion decision step which removes the block distortion by using a filter selected by the decision result by said first decision step when it is decided by the result by said second decision step that block distortion removal is necessary; 
 wherein said first decision step decides the strength of the block distortion by using an amplitude information of a motion vector which corresponds to a block neighboring to said block boundary; and 
 wherein said second decision step 
 decides that the removal of the block distortion is not necessary when said first decision step decides that there is no block distortion as the strength of the block distortion, and 
 decides that the removal of block distortion is not necessary when an absolute value of the difference of each pixel value corresponding to plural pixels which locate in the vicinity of said block boundary and belong to the same block is bigger than a predetermined threshold, even if said first decision step decides that there is a block distortion and the distortion is the strength of the predetermined block distortion. 
 
     
     
       2. A block distortion removal apparatus for removing block distortion included in the decoded image obtained by decoding the code sequences which are obtained by dividing an image into blocks each comprising plural pixels to be coded comprising:
 a first decision means which decides the strength of the block distortion at the block boundary: 
 a second decision means which decides the necessity or the innecessity of the removal of the block distortion by using the decision result by said first decision means; and 
 a block distortion decision means which removes the block distortion by using a filter selected by the decision result by said first decision means when it is decided by the result by said second decision means that block distortion removal is necessary; 
 wherein said first decision means decides the strength of the block distortion by using an amplitude information of a motion vector which corresponds to a block neighboring to said block boundary; and 
 wherein said second decision means 
 decides that the removal of the block distortion is not necessary when said first decision means decides that there is no block distortion as the strength of the block distortion, and 
 decides that the removal of block distortion is not necessary when an absolute value of the difference of each pixel value corresponding to plural pixels which locate in the vicinity of said block boundary and belong to the same block is bigger than a predetermined threshold, even if said first decision means decides that there is a block distortion and the distortion is the strength of the predetermined block distortion.